THE PHOSPHOINOSITOL PHOSPHATASE-ACTIVITY OF PTEN MEDIATES A SERUM-SENSITIVE G(1) GROWTH ARREST IN GLIOMA-CELLS

The PTEN gene (also called MMAC1 and TEP1) at chromosome 10q23 is muta ted in a variety of predominantly late-stage tumors and has been shown to suppress glioma cell growth in vitro and in vivo. Here we sought t o determine the mechanism by which PTEN mediates growth inhibition. Us ing the mutant PTEN glioma cell line, U87MG, as a transfection recipie nt for a series of PTEN alleles, we provide direct evidence that this capacity requires phosphatase activity. Mutations mapping upstream, wi thin, and downstream of the catalytic domain ablated activity toward a 3' phosphorylated phosphoinositide substrate of PTEN, whereas alleles with mutations flanking the catalytic domain retained activity toward the acidic protein polymer substrate, Glu(4)Tyr(1). Thus, catalytic a ctivity toward phosphoinositide substrates was required for growth sup pression, whereas activity toward the protein substrate was dispensabl e for growth suppression. Finally, we used apoptotic and cell prolifer ation analyses to show that PTEN-mediated growth inhibition under redu ced serum conditions was due to a G(1) cell cycle block rather than to an induction of apoptosis.